This invention relates to burn-in knives of the type commonly used in wooden furniture repair techniques.
A common technique for repairing chipped, gouged, or dented furniture involves the placement of hard plastic in the gouge, dent or depression in the wood in order to restore a smooth surface which may then be finished so as to look like the remainder of the wooden furniture. Typical of hard plastics used for this purpose are "No-Lift Stick", commercially available from Mohawk Finishing Products Inc., "NU GLO" patching stick, commercially available from Star Chemical Co., and common shellac stick. These materials are high-melting (e.g. 300.degree. F.-400.degree. F.) thermoplastics which are sold in stick or rod form.
Placement and working of the hard plastic in the gouge, dent, or depression in the furniture is typically effected by means of a burning-in knife (sometimes referred to as a "burn-in" knife). One type of burn-in knife is rather simple, having only an insulated handle (typically made of wood) and a blade having a working edge (which is generally a straight edge). This type of knife is brought to working temperature by placing the blade portion in a small furnace until it reaches the desired temperature.
Another type of burn-in knife is very similar in appearance to the first type except that it contains means permitting the blade to be electrically heated. For example, the knife may contain an electrical resistance heater which heats the blade in much the same manner as a soldering iron may be heated.
Both of the foregoing types of burn-in knives are conventional in the field and are available commercially, for example, from Mohawk Finishing Products, Inc.
The heated blade of the burn-in knife (whichever type of knife is used) is used to both (a) melt an appropriate amount of plastic from a plastic stick or rod, and (b) smooth the melted plastic into the gouge, dent or depression to be repaired. The smoothing step, in its final stages, is effected by supporting a portion of the working edge of the hot blade of the knife on the undamaged portion of the furniture adjacent to the damaged portion so that the melted plastic will be smoothed out level with the undamaged portion of the furniture. Thus, a portion of the working edge of the blade must also serve as an edge guide for the knife. This is necessary so that the repaired portion will not be out of the plane of the undamaged portion of the furniture.
A major disadvantage of such burn-in knives is that it is not possible to accurately and smoothly repair gouges, dents or depressions which are wider than the working edge of the blade of the knife. Also, when only a small portion of the working edge of the blade is functioning as an edge guide (i.e. resting on the undamaged portion of the furniture) extreme care must be exercised by the workman to maintain the working edge of the blade at a constant height over the melted plastic in the damaged portion so that no variations result in the finished plastic surface. There is also the danger of burning through the finish in the undamaged portion of the furniture adjacent to the portion being repaired. Care must also be taken to bring the knife down very gradually to the furniture surface while maintaining continuous horizontal motion of the knife. There is the further danger of interfering with previously repaired portions of the furniture if such repaired portions are adjacent to as-yet unrepaired portions. In such cases it is extremely difficult, if not impossible, to rest a portion of the hot edge of a blade on such a surface for guiding purposes.
Consequently, in view of the difficulties associated with the use of conventional burn-in knives there has been a great need for improvements in such burn-in knives. The present invention provides such improvements.